The long-term objective of this project is a combined biochemical and genetic analysis of the hormonal regulation of cell membrane characteristics relevant to neoplasia. These studies will focus on the glucocorticoid and cyclic nucleotide regulation of the serine protease, plasminogen activator, in HTC rat hepatoma cells in culture. HTC cells are a suitable experimental model for studying the hormonal regulation of membrane properties because of their well-characterized hormonal responsiveness and the availability of specific variant cell lines altered in hormone responsiveness. The glucocorticoid dexamethasone rapidly inhibits plasminogen activator activity, whereas cyclic nucleotides dramatically stimulate activator activity; paradoxically, dexamethasone enhances this stimulation. We have demonstrated that the glucocorticoid inhibition is secondary to the induction of a soluble inhibitor specific for plasminogen activation. We have isolated a unique set of variant HTC cell lines selectively resistant to the dexamethasone inhibition, which fail to make inhibitor when incubated with glucocorticoids. In this project we plan to characterize biochemically and immunologically the multiple molecular weight forms of plasminogen activator in HTC cells. We will analyze the regulation of plasminogen activator activity and synthesis by glucocorticoids and cyclic nucleotides, and explore the mechanisms by which these hormonal factors might interact. Finally, we will attempt to isolate and characterize the glucocorticoid-induced inhibitor of plasminogen activation and study its hormonal regulation. Limited proteolysis mediated by the plasminogen activator-plasmin cascade plays a significant role in the behavior of transformed cells as well as in many normal processes. These studies should increase our understanding of the hormonal regulation of this important cell membrane property and of the membrane biology of neoplastic cells.